eosc 114 - waves + tsunamis

What is the shape of the coast line dependent on?

-many processes of varying time scales

Sediment transport and deposition

Erosion

Uplift and subsidence

how is the ocean linked with the atmosphere, and what is the difference between waves and surface currents?

When wind blows over the ocean, it drags on the surface and transfers energy from the atmosphere to the water, thus creating waves and currents. Very large scale, permanent winds that blow over the ocean produce surface currents, which transport both matter (water) and energy. Winds that blow occasionally or over smaller areas produce waves, which transport energy in the direction of the wind

how do we define waves?

The mechanical expression of energy

describe the anatomy of a wave (crest, trough,wavelength, amplitude, period, frequency, speed)

-Crest and trough are the highest and lowest point respectively

-Wavelength is the distance between two successive crests or troughs

-Amplitude is the vertical distance between trough and calm sea level

-Period is the time for one wavelength to pass a point

-Frequency is the number of waves which pass a point in a unit of time

-speed or celerity is the distance traveled for a unit of time

What is steepness and how is it measured?

a measure of the "peakedness" of a wave; the ratio of Height to Wavelength, H / L; (no units)

What is wave energy related to and what is the constriction in this relationship?

The energy transported by waves is related to the wave height, H, waves with great heights transport more energy. This simple correlation applies only to deep-water waves

Usually, though not all the time, waves with great heights also have long wavelengths.

How is wave period related to other wave characteristics?

A) Period = Frequency

B) Period = Frequency ÷ Wavelength

C) Period = 1 / Frequency

D) Period = 1 / Wavelength

E) Period = 1 / Celerity

C) Period = 1 / Frequency

what is Generating/Disturbing Force and what do we use it for?

Generating force is the force that causes a wave to form and we use it to classify different types of waves.

what are the four different waves based on generating force?

Wind wave-wind over water

Seiche-changes in atmospheric pressure

Tsunami- Faulting of sea floor, undersea volcanic eruption, landslide into ocean

Tide-Gravitational attraction between earth-sun and earth-moon; rotation of earth

what is restoring force and how do we use it?

Restoring force is the force that returns a wave to its resting state and we use it to classify different waves

what are the two waves classified by restoring force?

Capillary wave-surface tension

Gravity-surface gravity waves (Wind wave, seiche, tsunami, tide)

What are capillary waves and how do they aid in the generation of wind driven waves?

Capillary waves are tiny waves with wavelengths about the size of your fingernail and are restored by surface tension.

The wind pushes the surface "skin" of the ocean and a series of small wrinkles, the capillary waves, develops. As the wind speed increases, or as wind blows over longer periods of time and over the same area, more energy is transferred to the surface ocean and the waves grow larger.

What is sea state?

An assessment of the ocean's conditions or the roughness of the ocean surface

The amount of energy transferred to the ocean can be estimated by the height of the waves produced.

what three factors does sea state depend on?

-Wind strength/speed

-Fetch

-Wind duration, the length of time that the wind has been blowing over the fetch

As wind energy transfers to the ocean, what are the wave stages or development?

Capillary waves to ripples to chop to fully developed

What is a fully developed fetch?

A specific fetch in the ocean is said to be fully developed once it has absorbed the maximum amount of energy it can contain

The waves of a fully developed sea can achieve the maximum height possible for a given wind speed, fetch and duration of wind.

What happens if additional energy is added to a fully developed fetch?

any additional energy input by the wind is balanced by energy dissipated by breaking waves. Waves in this condition are chaotic, where there are waves of varying heights, lengths, speed, and direction.

How are waves sorted as they move away from a fetch?

They are sorted by speed and wavelength (longer wavelength is related to more speed). Thus the waves with the longest wavelength and fastest speed leave the fetch first. The last waves to leave are the slowest and shortest waves

What are swells and wave trains?

When waves leave a fetch in an organized manner they are called swells. Swells propagate away from the fetch in groups called wave trains

What conditions in a fetch lead to the highest energy waves?

The stronger the wind and the longer the duration the wind is blowing over the largest of fetch, the greater the maximum wave heights achievable in that patch of ocean.

The largest wind-driven waves develop in the Southern Ocean around Antarctica. In which of the following factors does the Southern Ocean have the biggest advantage over anywhere else in the world?

A) Amount of ice cover over the ocean

B) Wind speeds over the ocean

C) All waves are moving at the same speed

D) Fetch

D) Fetch

why do we often measure wave height?

information on sea state is important in the real world, such as for the ocean transportation sector or in forecasting storms. Wave height is the most commonly tracked parameter of sea state because it is easily measured and it a good indicator of wave energy

significant wave height

the average height of the highest one-third of the waves

Because the significant wave height is an average number, we expect to encounter a group of waves whose maximum wave height can be up to twice the significant wave height

how do you estimate significant wave height?

a) List all the wave heights observed in descending order (tallest wave to shortest wave);

b) Select n of the tallest waves, where n is equal to one-third of the number of waves observed;

c) Calculate the average wave height of your selected waves

what is the Beaufort Scale?

A qualitative measure of sea state with 13 conditions. It is a measure of the intensity of the wind based on human observations of the sea state

The modern version of the Beaufort Scale still lists 13 conditions but are now mainly based on the wind speeds that produce the qualitative description of the effect of the wind at sea and on land

What Beaufort scale would call for a small craft advisory? A gale warning? A storm warning? A tropical storm warning? and a Hurricane or cyclone warning?

small craft advisory- Beaufort 6 or 7

gale warning-Beaufort 8 or 9

storm warning- Beaufort 10 or 11

tropical storm warning- Beaufort 8 to 11

Stronger winds result in a hurricane/cyclone warning

(there is nothing about the beaufort scale in the LOs but if you want to look at the different conditions there are some pictures about halfway through the first lesson in waves)

When a wave passes by a patch of ocean water, what happens to the individual water particles?

-waves do not transport matter, just energy

-the water particles move forward and downward in the direction of the wave propagation as a crest passes and backward and upward as a trough passes (tracing an orbital motion)

-the net movement of the particles is zero

What is a wave base?

As waves pass through water they move the particles. the wave base is the lowest particles below a wave surface that experience motion. wave base is calculated as;

Wave Base = L/2

where L is the wavelength

Deep water waves

Deep-water waves are waves that are traveling in ocean depths d equal or deeper than L ÷ 2

These waves do not "feel the bottom" because their wave bases are shallower than the depth of the ocean they are passing through

Shallow water waves

Waves travelling in areas where the water depth d is equal or shallower than L ÷ 20